Input variable precedence order in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the highest precedence source for Terraform input variables?

Command-line flags (e.g., -var or -var-file) have the highest precedence and override all other sources.

intermediate

List the order of precedence for Terraform input variables from highest to lowest.

1. Command-line flags (-var, -var-file) 2. Environment variables (TF_VAR_name) 3. terraform.tfvars files and other tfvars files 4. Default values in variable blocks

beginner

How do environment variables affect Terraform input variables?

Environment variables prefixed with TF_VAR_ set the value of input variables and override values from tfvars files and defaults, but are overridden by command-line flags.

beginner

What happens if a variable is not set by any source in Terraform?

Terraform uses the default value defined in the variable block. If no default is set and the variable is required, Terraform will prompt the user for input.

intermediate

Why is understanding input variable precedence important in Terraform?

It helps avoid unexpected values by knowing which source will override others, ensuring predictable and controlled infrastructure configuration.

Which source has the lowest precedence for Terraform input variables?

A Environment variables

B Default values in variable blocks

C terraform.tfvars files

D Command-line flags

Default values in variable blocks have the lowest precedence and are used only if no other source provides a value.

If a variable is set in both an environment variable and a terraform.tfvars file, which value does Terraform use?

A Value from terraform.tfvars file

B Value from default in variable block

C Terraform will throw an error

D Value from environment variable

Environment variables override values set in terraform.tfvars files.

How can you override a Terraform variable value without changing any files?

A Pass the value using a command-line flag

B Use a terraform.tfvars file

C Terraform does not allow overriding without files

D Set a default value in the variable block

Passing variables via command-line flags overrides all other sources.

What prefix must environment variables have to set Terraform input variables?

A TF_VAR_

B TF_INPUT_

C TERRAFORM_VAR_

D VAR_

Environment variables must be prefixed with TF_VAR_ followed by the variable name.

If a required variable has no default and is not set by any source, what does Terraform do?

A Uses a null value

B Throws an error and stops

C Prompts the user to enter a value

D Uses an empty string

Terraform prompts the user to input a value for required variables without defaults.

Explain the order in which Terraform applies input variable values from different sources.

Think about which source you would want to override others when running Terraform.

Describe what happens when a Terraform variable is not set anywhere and has no default value.

Consider how Terraform ensures required variables have values.